Abstract: Provided are a method and an apparatus for measuring the spectral intensity and phase of a light pulse having an arbitrary time duration. The apparatus includes: a nonlinear mixing means for generating a signal light pulse expressed by the following Formula (? denotes an operator representing general nonlinear mixing, and ? denotes a coefficient which is proportional to a nonlinear susceptibility in the nonlinear mixing) by nonlinearly mixing a reference light pulse having an electric field Er(t??) delayed by an optical delay means and a measurement target light pulse having an electric field E0(t); and Er(t??)+?Er(t??)?E0(t) an imaging spectrum device for spectrally splitting the signal light pulse and outputting a Fourier transform signal expressed by the following Formula (F denotes a symbol indicating Fourier transform, * denotes a complex conjugate, and R denotes a symbol indicating a real part), |F[Er(t??)]|2+|?F[Er(t??)?E0(t)]|2+2R{?F[Er(t??)]*·F[Er(t??)?E0(t)]}.